Insert hyphens in javascript

Quickest way would be with some regex:

Where n is the number

n.replace(/(\d{3})(\d{3})(\d{4})/, "$1-$2-$3");

Example: http://jsfiddle.net/jasongennaro/yXD7g/

var n = "1234567899";
console.log(n.replace(/(\d{3})(\d{3})(\d{4})/, "$1-$2-$3"));

Given this kind of input, an other way would be:

var phone = "1234567890";
phone = phone.replace(/(\d{3})(\d{3})(\d+)/, '$1-$2-$3');

Of course this does not work if your input changes.